ERBB2 and neoplasm: In 2017, Hou et al. evaluated tumors with incomplete treatment response to HER2-directed NAC; HER2 heterogeneity was identified more frequently in these cases compared to those who had a pCR [29] Although we did not evaluate tumors for HER2 heterogeneity after NAC, both patients in our study with known tumor heterogeneity before NAC had significant disease burden (RCB-II) after HER2-directed NAC.